Electrolytic condenser and method of preparing etched electrodes therefor



UNITED STATES PATENT OFFICE ELECTROLYTIC CONDENSER AND METHOD OFPREPARING ETCHED ELECTRODES THEREFOR Samuel Ruben, New Rochelle, N. Y.

No Drawing. Application July 2, 1936, Serial No. 88,533

7 Claims. (Cl. 175-315) This invention relates to the method of pretiontends to dissolve the foil and if the maxiparing etched surfaces andparticularly etched mum benefit arising from the increased areaobelectrodes for electrolytic devices. tained by a deep etching isdesired, it is neces- The present application is a continuation-insaryto use a much thicker foil than would otherpart of my co-pendingapplication, Serial Numwise be required. Furthermore, care must be exher734,134, filed July 7, 1934 now Patent No. ercised to prevent theetching from being too 2,066,912. deeply applied. These limitations areavoided by An object of the invention is to improve the the method ofetching and the type of electrodes methods of preparing etched metalsurfaces. used.

Another object is to provide an etched electrode My invention comprises,in its preferred form for electrolytic devices, such as electrolyticcona novel method of preparing etched electrodes for densers.electrolytic condensers, said electrodes being Other objects of theinvention will be apparent formed of a metalsuch as aluminum or tantalumfrom the following description taken in connecupon which it is possibleelectrolytically to form v tion with the appended claims. acurrent-blocking film after etching. These 16 The present inventioncomprises. the combinametals may be in any suitable form for use, fortion of elements, methods of manufacture, and example, as foil W By theuse 0! W e the product thereof brought out and'exemplified stead of foilelectrodes, the limitation'on deep in the disclosure hereinafter setforth, the scope etching is removed and an exceptionally large of th iention being indicated in the appended effective current blocking areais made available 2 claims. While a preferred embodiment of the withoutsubstantially weakening the electrode invention is described herein, itis contemplated structure. It will be seen that by using an aluthatconsiderable variation may be made in the minum wire having a diameterin the order of method of procedure and the combination of .040" or anarrow aluminum tape of the same elements without departing from thespirit of thickness and prefe y not Wide,

the invention. that it is possible to obtain a very deep etching Dryelectrolytic condensers have heretofore utiwith consequent increasedfilm blocking area. lized sheet foil electrodes usuallyv of. aluminumThe impurities in commercial aluminum are ranging in thickness from.002" 110 .004" and in chiefly iro a Silicon. although inor amountswidth from one inch to three or four inches. of copper ar sometimesfound- In t A rad These foils have been spaced by a reticular cloth thealuminum content will normally average spacer such as disclosed in myUnited States Letabout 99.2 per ce t, w Silicon Varying m 5 ters Patent1,710,073 and 1,714,191, or by paper' o 0- 0 per ent nd ir n v ryin from0.25 to spacer as shown in my United States Letters pe c te iron contentis usually ate Patent 1,891,206, or by a regenerated sheet eelluthan thesilicon content. Copp Will Vary from lose spacer, for instance,Cellophane as illusa trace only tODVeI D cent- SOdiU-m i in trated in myUnited States Letters Patent recent years found only in traces ifpresent at 1,918,716. In -the construction of these cona With rad A t ps t metal is enerde sers a spacer of approximately the same diallyreserved for manufacture of electrical conmensions as the foils, isplaced on each side of ductors on account of its lower electricalresistiv- 0 one of the electrodes and the two foils and spacy-Electrolytic d o is of y high ers are then rolled, usually incylindrical form; Pu ty, uc as 9 to pu alum um- Prior to rolling thespacer is impregnated or per- According t0 On feature of y invention tmeated with a viscous electrolyte so as to afford et g s Co e 50 as tavoid tOO great a a conductive path between the electrode foils, dllct min mass Of t e elect ode metal during although in some cases thecondenser roll is asetching by providing, instead of substantially puresembled and the electrolyte thereafter introduced metals, an alloy ofsuc Composition as t Obtain by impregnation. a selective etching action.For example, I pro- It has been long known in the art that if the poseto substitute for the pure aluminum foil elecaluminum plates are etchedor otherwise roughtrodes of the prior art, an aluminum alloy havingened, an increased capacitance is obtained due a content of a materialreadily soluble in an etchto increased surface and lower average oxidefilm ing agent which does not substantially dissolve thickness formed onsuch etched plateh aluminum, suchas nitric acid. For example, add-However, the employment of an etching process ing 10% magnesium to thepure aluminum and is limited, due to the fact that theetching'soluetching the electrode in nitric acid, the magneu slum israpidly etched out and the aluminum, other than becoming slightlyoxidized on its surface, is unaffected. For the usewith a nitric acidetching agent, an alloy of aluminum with one or more of the metals,calcium, lithium or beryllium may be substituted for thealuminum-magneslumv alloy electrode. Neither magnesium, calcium, lithiumnor beryllium is present as impuri ties in electrolytic condenser foilor other grades of commercially pure aluminum.

Generally, it may be stated, with the film forming metal used, wheth eraluminum or tantalum, that the material alloyed therewith, should be onewhich is readily capable of being etched out or dissolved by the etchingcompound and that the etching compound itself should be such as not toadversely attack or affect the film forming metal base. For instance, inplace of the nitric acid I may use sulphuric acid, chromic acid or anacid salt such as aluminum ammonium sulphate.

The foil or wire may be prepared as follows for use as electrodes forelectrolytic condensers: The foil or wire of aluminum-magnesium alloy ispassed through hot nitric acid and the etching accomplished by thedissolving of the magnesium. The etched foil or wire is then filmformedby the customary continuous formation "dry" and "we electrolyticcondensers.

While the present invention, as to its objects and advantages, has beendescribed herein as carried out in specific embodiments thereof, it isnot desired to be limited thereby but it is intended to cover theinvention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An'electrode for electrolytic condensers and the like composed ofaluminum of a purity of at least 99.2% having magnesium intentionallyalloyed therewith, said magnesium being present in a relatively smallbut appreciable amoimt, said electrode having an etched roughenedsurface resulting from the removal of the magnesium from said surfacewhereby the effective film forming surface of said electrode is greatlyincreased.

2. An electrode for electrolytic condensers and the like comprising purealuminum having intentionally alloyed therewith a relatively smaller butappreciable amount of magnesium, said electrode having an etchedroughened surface resulting from the removal of the magnesium from saidsurface.

3. In the process of providing film forming electrodes for electrolyticcondensers and the like, the steps of combining with a pure film formingmetal such as aluminum, a relatively smaller but appreciable quantity ofmagnesium, thereafter exposing said metal composition to the action ofan etching solution to remove said magnesium from the surface thereof.

4. In the process of providing film forming electrodes for electrolyticcondensers and the like, the steps of combining with pure aluminum, arelatively smaller but appreciable quantity of magnesium, thereafterexposing said metal composition to the action of nitric acid to removethe magnesium from the surface thereof.

5. In the process of providing film forming electrodes for electrolyticcondensers and the like, the steps of combining with pure aluminum, arelatively smaller but appreciable quantity of magnesium, thereafterexposing said metal composition to the action of sulfuric acid to removethe magnesium from the surface thereof.

6. An electrode for electrolytic condensers comprising aluminum and arelatively muchsmaller amount of magnesium, said electrode having anetched surface of high effective electrical capacity resulting from theremoval of the magnesium therefrom, and a dielectric oxide film on saidsurface.

7. An electrolytic condenser comprising two electrodes and anelectrolyte, one of said electrodes comprising aluminum, and arelatively much smaller amount of magnesium. said dectrode having anetched surface of high effective electrical capacity resulting from theremoval of the magnesium therefrom, and a dielectrlc'oxide film on saidsurface.

SAMUEL RUBEN.

